Cleanest U.S. Cities for Ozone Air Pollution 2007

Ozone acts as a powerful respiratory irritant at the levels frequently found in most of the nation's urban areas during summer months. Symptoms include shortness of breath, chest pain when inhaling deeply, wheezing, and coughing. A study of a sample of longtime residents of Los Angeles, which has the highest and most frequent ozone problem in the nation, found that the group had a higher-than-expected loss of lung function over time.